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BMX SERIES III CONSOLE
8.2.2 TD-171 Digital Slave Clock
The TD-171 Digital Slave Clock is a six-digit (hours, minutes, seconds) digital display specifically
designed to operate with an ESE or compatible master clock time code generator. It is constructed in an
aluminum case for shielding, uses an external power supply (PR&E #50-17, supplied with the clock), and
is designed specifically for use in PR&E consoles. Power and master clock connection are made to the rear
of the unit.
TD-171
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FIGURE 8.2 TD-171 DIGITAL SLAVE CLOCK
CIRCUITRY
The TD-171 circuit is virtually the same as the ESE model ES-171 unit (the TD-171 is manufactured with
the express consent of ESE). The time code consists of 24 bits of pulse width modulated data. A wide pulse
(260 microseconds) represents a binary one (1), and a narrow pulse (65 microseconds) represents a binary
zero. The data rate is 60 Hz.
Demodulation is accomplished using shift registers U3, U4 and U5. The incoming data is buffered by
transistor Q2 and gate U1 before it is fed to shift register U3. One of the one-shots of dual monostable U2
is used to clock the shift registers. The pulse width of this one-shot is set to be 2.5 times the pulse width
of the narrow data pulse. As a result a "one" or "zero" will be clocked into U3 depending on the width of
the data pulse.
The second one-shot of U2 is retriggered by each data pulse until the completion of all 24 bits of data. U2
then times out and triggers another one-shot, formed by two gates of U1. This transfers the data from the
shift register outputs to the latches contained in decoder/drivers U6 through U11, prior to the next
transmission of data. This completes the serial-to-parallel conversion. The decoder/drivers and displays
then translate the parallel BCD information into the visual time display.
REVISION B
204
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